1. Field of the Invention
The invention relates to a refrigeration cycle apparatus. More particularly, the invention relates to technology that estimates the torque required to drive a compressor provided in a refrigeration cycle apparatus.
2. Description of the Related Art
A refrigeration cycle apparatus for air-conditioning a vehicle typically includes a compressor that compresses refrigerant, a condenser, a receiver (i.e., a gas-liquid separator), an expansion valve (i.e., a pressure-reducing mechanism), and an evaporator. The compressor, the condenser, the receiver, the expansion valve, and the evaporator are connected in a loop by refrigerant piping. Refrigerant discharged from the compressor flows to the condenser, from the condenser to the receiver, from the receiver to the expansion valve, and from the expansion valve to the evaporator, after which it is drawn back into the compressor.
Incidentally, when driving the compressor using an engine mounted in the vehicle, the compressor becomes a load on the engine so the engine requires extra energy to drive the compressor. Therefore, in order to reduce the fuel consumption of the vehicle, the output of the engine must be controlled based on the operating state of the compressor that becomes an engine load. That is, the torque required to drive the compressor is taken into account and the engine output is controlled to generate that much extra torque. For example, when the engine is idling, engine output control such as idle-up control is performed in which the engine speed is increased just enough to generate the amount of extra torque required to drive the compressor. Therefore, when driving the compressor using the engine, it is important to accurately estimate the torque required to drive the compressor.
The torque required to drive the compressor can be estimated based on the refrigerant flowrate and the discharge and intake pressures of the compressor, as is described in Japanese. Patent Application Publication No. 2004-175290 (JP-A-2004-175290), for example. Also, a flowrate control valve is provided in the high pressure region of the refrigeration cycle apparatus (i.e., in the region between the discharge port of the compressor and the inlet of the expansion valve), and the torque required to drive the compressor is estimated based on a refrigerant flowrate determined by an indicated value (i.e., a current value) of this flowrate control valve (i.e., an indicated flowrate).
However, with a structure in which the torque required to drive the compressor is estimated based on an indicated flowrate according to an indicated value of a flowrate control valve as described above, there may be a difference between the indicated flowrate and the actual refrigerant flowrate during a transition when, for example, the intake pressure of the compressor fluctuates due to a change in the temperature in the evaporator or the like, or when the indicated value changes. As a result, the torque may not be able to be accurately estimated. Also, a difference may also occur between the indicated flowrate and the actual refrigerant flowrate due to a change in the characteristics of the flowrate control valve or the like. Moreover, during startup of the compressor, the actual refrigerant flowrate does not increase until the refrigerant accumulated in a control pressure chamber has all been discharged, so there is a difference between the indicated flowrate and the actual refrigerant flowrate during this time. Incidentally, also in the refrigeration cycle apparatus of the related art described above, the torque required to drive the compressor is estimated using the refrigerant flowrate determined by the current value supplied to a capacity control valve of the compressor, so a similar problem may occur in a case such as that described above.